1. Field of the Invention
The present invention relates to a technology for transferring image data from a storage device to a display device for displaying the image data.
2. Description of the Related Art
As a technology to display large image data for browsing, a typical image processing apparatus compresses original image data, and stores therein the compressed image data having a file size smaller than the original image data. The typical image processing apparatus displays on a display unit the image data that is obtained by decompressing the stored compressed image data (see Japanese Patent Application Laid-open No. H5-191762 and Japanese Patent Application Laid-open No. H6-171151).
The compression is a process of coding the image data on a file basis or a block basis, thereby creating a bitstream of the compressed image. The bit size of most of the bitstreams of the compressed images is not large enough to display the image with an uncompressed format.
An advantage of the compression process is that a memory space occupied by the compressed image data on a recording medium, such as a random access memory (RAM), a disk, and a magnetic tape, is smaller than that occupied by uncompressed image data. Moreover, the compression process is effective from the viewpoint of data transfer. The smaller bitstream of the compressed image is transferred in a shorter time than a time that it takes to transfer the uncompressed image.
However, if only the compressed image data having the smaller file size is stored in the image processing apparatus, a decompression process is always required before displaying the image. Therefore, it takes a long time to display the image, which disadvantageously decreases a speed of browsing the image data.